Emails erroring with "Invalid login: Username and Password not accepted"

This error usually means your Google app password was deleted after a password change.

For the full recovery steps, see Reconnect your email sender, which covers Gmail, Microsoft 365, and test connection checks.

If you use Microsoft 365, the cause is usually a disabled SMTP AUTH setting rather than a password problem. See Why am I getting an 'Invalid login: 535' error with Microsoft 365?.